Patterns of photoinduced oxygen atom transfer from triplet nitro compounds to a number of methyl substituted hydrazines

Photochemical methods of oxidation of organic compounds attract attention due to the possibility of carrying out processes at low temperatures. These methods are particularly relevant in the context of the utilization of alkyl–substituted hydrazine derivatives, a class of persistent supertoxidants. The use of triplet nitro compounds as photochemical oxidants opens up the prospect of implementing “green” approaches to the processing of nitrogen-containing waste. Previously, we studied the mechanism of oxidation of asymmetric dimethylhydrazine, but the systematic influence of the degree and position of methylation on the energy and geometry of the transition state remained unclear. Quantum chemical calculations were performed by the Gaussian 09 program using density functional theory (DFT). Hybrid B3LYP and ωB97XD functionals were used in combination with various basic sets. The search for transition states was carried out using synchronous transit (TS) methods, followed by the reaction coordinate (IRC) calculating. A comparative analysis of the oxygen atom transfer reaction from triplet nitro compounds to hydrazine, monomethylhydrazine, symmetric dimethylhydrazine, asymmetric dimethylhydrazine and trimethylhydrazine was performed. A pattern has been established: the introduction of a methyl group onto the attacked nitrogen atom reduces the energy barrier due to the induction effect, whereas steric shielding of the reaction center during methylation of a neighboring nitrogen atom, on the contrary, increases it. The analysis of the spin density distribution confirms the biradical mechanism for all considered systems. The results can be used in the development of selective and environmentally friendly methods for the photochemical disposal of toxic nitrogen-containing compounds.